There's an eye in the sky, I'm tryna let y'all know

By saying there’s an eye in the sky Pharrell is referencing his previous line about drones, and is trying to say people are watching through these drones.

More specifically, the government trying to catch him moving some serious ass weight!

In an alternate interpretation, Pharrell could be doing double-duty with “eye in the sky.” He is warning other rappers to let go of excessive hoes and cars because there’s an eye in the sky (God) watching them. That’s why he’ll be setting standards, letting war go, and pursuing the boom business.

“I’m Christian…I ain’t been [to church] in so long, man. But God knows my heart. I have conversations with God a few times every day… I spend more time thanking [the Lord] for the shit I don’t have than the things I do got."
He desires not to get "caught up in worldly things…I don’t worry about things like that,” he says.

His views on this seem to have changed about as much as his looks based on this late 2013 article..